This application is based upon and claims benefit of priority of Japanese Patent Application No. 2000-367474 filed on Dec. 1, 2000, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a magnetic switch of a starter motor for cranking an internal combustion engine.
2. Description of Related Art
A frame of a magnetic switch is usually formed by cold-forging or pressing an iron material into a rough shape and then machining some portions into exact dimensions for holding inner parts therein. When the frame is integrally formed in this manner, magnetic resistance in a magnetic flux path can be made small. However, a costly machining process is required in this method. On the other hand, there is another method of forming the frame, in which the costly machining process of the frame is eliminated and separate parts constituting a magnetic flux path are assembled. When this method is employed, however, there is a problem that a magnetic resistance in the magnetic flux path becomes high. This is because the magnetic resistance at contacting surfaces of separate parts becomes high. If the magnetic resistance in the magnetic flux path is high, a high performance of the magnetic switch cannot be attained.
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved magnetic switch of a starter motor, employing an assembled frame structure in which the magnetic resistance in the magnetic flux path is suppressed.
A magnetic switch is used for closing or opening an electrical circuit for supplying electrical power to a starter motor. The magnetic switch includes a pair of stationary contacts, a movable contact for closing or opening the stationary contacts, and an electromagnetic actuator for driving the movable contact. The electromagnetic actuator includes a coil for generating a magnetic flux, a magnetic core member for providing a magnetic flux path for the coil, and a plunger for driving the movable contact upon energization of the coil. A switch cover forming a switch chamber in which the pair of stationary contacts and the movable contact are disposed is connected to the magnetic core member.
The magnetic core member is composed of a first core, a cylindrical yoke and a second core. All the components of the magnetic core member are contained together in a cup-shaped frame by peening an open end of the cup-shaped frame, so that they firmly contact one another not to increase the magnetic resistance in the magnetic flux path. The cup-shaped frame has a bottom wall and a cylindrical portion, and a squeezed portion having a smaller diameter is formed in the cylindrical portion next to the bottom wall. The disc-shaped first core is forcibly inserted in the squeezed portion of the frame.
The cylindrical yoke is made by rounding a flat plate into a C-shaped body having a small opening and an outer diameter a little larger than an inner diameter of the cylindrical portion of the frame. The C-shaped body is forcibly inserted into the cylindrical portion by squeezing the small opening. The second core is also inserted in the cylindrical portion of the frame. Components forming the magnetic core member are all pressed together by an axial force generated by peening an outer periphery of the cylindrical portion of the frame.
The switch cover is pushed against the magnetic core member and connected thereto by peening the open end of the frame. The axial force pushing the switch cover against the magnetic core member is set to a lower level than the axial force connecting together the components of the magnetic core member, so that the close contact of the components is not loosened by pressing the switch cover toward the magnetic core member. The thickness of the disc-shaped first core is made smaller the depth of the squeezed portion of the frame to secure a close contact between the first core and the cylindrical yoke.
The switch cover is pushed against the magnetic core member and connected thereto by caulking the open end of the frame. The axial force pushing the switch cover against the magnetic core member is set to a lower level than the axial force connecting together the components of the magnetic core member, so that the close contact of the components is not loosened by pressing the switch cover toward the magnetic core member. The thickness of the disc-shaped first core is made smaller the depth of the squeezed portion of the frame to secure a close contact between the first core and the cylindrical yoke.
According to the present invention, increase of the magnetic resistance in the magnetic flux path is minimized, though the magnetic core member forming the magnetic flux path is composed of separate components.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiments described below with reference to the following drawings.